This study explored the process and outcomes of constructivist methods of enhancing science understanding in the topic areas of light and the earth in space. The sample was drawn from a group of 41 nine-year-old children, delivered in four two-hour weekly sessions. Each session involved different combinations of interactive discussion and practical investigative activity. Criterion-referenced pre- and post-intervention assessment indicated very large gains in participant understanding. These gains were promoted by building upon participant prior understanding, use of attuned questioning and scaffolding by an adult, and undertaking structured practical science investigations. The study showed that gains in complex learning outcomes could be achieved using a combination of scaffolding and building together with practical activities. The implications for classroom practice are discussed. (Contains 5 figures and 5 tables.)